Technical Field
The present invention relates to a lockup device, particularly to a lock-up device for a torque converter, which is disposed between a front cover coupled to an engine-side member and a torque converter body in order to directly transmit a torque from the front cover to a turbine of the torque converter body.
Background Art
A torque converter is embedded with a lock-up device in order to reduce fuel consumption. The lock-up device is disposed between a front cover and a turbine, and is configured to mechanically couple the front cover and the turbine in order to directly transmit a torque therebetween.
In general, the lock-up device includes a piston and a damper mechanism. The piston is pressed onto the front cover by the action of hydraulic pressure, and a torque is transmitted to the piston from the front cover. On the other hand, the damper mechanism includes a plurality of torsion springs, and the piston is elastically coupled to an output-side member coupled to the turbine by the plural torsion springs. In the lock-up device as described above, the torque transmitted to the piston is transmitted to the output-side member through the plural torsion springs, and is further transmitted to the turbine.
Incidentally, Japan Laid-open Patent Application Publication No. 2009-293671 describes a lock-up device that an inertia member is mounted to the output-side member in order to inhibit variation in engine rotation. In the lock-up device described in Japan Laid-open Patent Application Publication No. 2009-293671, the inertia member is mounted to the output member fixed to the turbine so as to be rotatable relatively thereto. Furthermore, torsion springs are mounted as elastic members between the output member and the inertia member.
In the lock-up device of Japan Laid-open Patent Application Publication No. 2009-293671, the inertia member is coupled to the output member through the torsion springs. Therefore, the inertia member and the torsion springs function as a dynamic damper, and these components attenuate variation in rotational speed of the output-side member (turbine).
On the other hand, Japan Laid-open Patent Application Publication No. 2012-87856 describes a lock-up device to be implemented by installing a mechanism for generating a variable, hysteresis torque in a position between the inertia member and the output member within the lock-up device as described in Japan Laid-open Patent Application Publication No. 2009-293671. Even when a lock-up rotational speed is set to be low, the lock-up device can inhibit variation in output-side rotational speed over wide rotational speed ranges.